The present invention involves a process for conversion of aluminum oxide hydroxide (AlOOH) to aluminum oxide, also known as alumina. More specifically, the invention involves a much lower temperature process for conversion of AlOOH to alumina than the previous state of the art process.
Aluminum oxide hydroxide AlOOH-Boehmite or Pseudoboehmite (PB) is the most used precursor in the production of alumina porous supports and certain catalysts. The currently used technologies employ heat treatment of PB to decompose it to the oxide. Temperatures as high as 600° C. are needed because of the thermal stability of the PB alumina phase. There is a loss of BET surface area and pore volume in the course of the heat treatment. There is a need of technologies for efficient conversion of Boehmite to high quality aluminum oxide.
Dawsonite, sodium aluminum dihydroxide carbonate (NaAlOH)2CO3) and its alkali metal analogs are useful compounds that either occur naturally or are synthesized by a variety of processes which in the prior art have taken place in aqueous medium. In U.S. Pat. No. 4,356,157, dawsonite was produced by combination of aluminum hydroxide and an alkali metal or ammonium hydrogencarbonate at high pressure and at temperatures between 150° and 250° C.
Pseudoboehmite is a microcrystalline alumina, and it usually possesses a relatively high surface area with high pore volume which makes this type of alumina highly desirable for the preparation of catalyst supports. Pseudoboehmite is generally prepared by the reaction of an aluminum salt with a strong base; or by the reaction of a strong acid with a basic aluminum salt under carefully controlled pH and temperature. Both batch and continuous processes of pseudoboehmite precipitation are industrially practiced. Usually, the spray drying of a slurry is the final step in the process. Depending upon the conditions, the spray drying process yields pseudoboehmite powders consisting of particles having an average particle size from about 10 to about 80 microns. In most of the cases the particles are composed of numerous subagglomerates with much smaller size.
Pseudoboehmite may be prepared from dawsonite as disclosed in U.S. Pat. No. 3,730,062 by hydrothermal conversion at temperatures of about 80° to 150° C.